Burner control system



Sept. 2, 1941.

V. R. TATE BURNER CONTROL SYSTEM INVENTOR.

Patented Sept. 2, 1941 BURNER CONTROL SYSTEM Virgil Robins Tate, Milwaukee, Wis., assigner to Perfex Corporation, Milwaukee, Wis., acorporation of Wisconsin Application october 24, 193s, seria1No.236,c55 (ol. 158;-28)

23 Claims.

This invention relates in general to burner control systems and apparatus, but more particularly to an improved burner control means, and the principal object of the invention is to provide a burner control device which is economical to manufacture, comprises few parts and a simple arrangement of elements, and is reliable and simple in operation.

In burner control systems it is customary to provide some safeguarding means such as a safety or lockout switch which will, in case of ignition or ame failure, shut down the burner until the switch has been manually reset. The safety lockout switch usually consists of a switch element, a bimetal actuator, and an electric heater for the bimetal actuator. In case the electric heater is permitted to remain energized for too long a period, the bimetal actuator opens the switch. The electric heater is usually energized when the burner is started, and subsequently, upon the establishment of combustion conditions the burner, the heater is deenergized by either opening its circuit or short circuiting the same. It is customary to provide a combustion responsive or stack switch to control the circuit of the heater. The circuit for the burner motor is also usually controlled by a relay having its winding energized in a low voltage circuit with the electric heater in series therewith, or the heater may such a manner so as to cooperate with the stack switch operation to operate the safety switch.

A further object is to eliminate the electrical control of the bimetal heater by the stack switch operation and reduce the number of electrical controls and switching operations in a burner system. A further object is to provide a circuit arrange ment for a burner control system in which the bimetal safety switch heater is energized in a circuit which is independent of the energizing circuits of the burner means so that the heater will not be effected by the operation of the same. With the foregoing and other objects in view the invention consists in the construction, ar-

rangement, combination and circuit arrangement of the various parts of the control apparatus and system, whereby the objects contemplated are attained, as hereinafter fully set forth, pointed out in the claims, and illustrated in theaccompanying drawing.

In accordance with the objects of the invention a preferred embodiment of the invention is disclosed in the apparatus and circuits shown on the accompanying drawing in which;

Fig. 1 discloses a cross-sectional side elevation of the burner control apparatus of the invention with the elements shown in their normal inactive or cold position;

Fig. 2 discloses a fragmentary portion of the Fig. 3 is a similar view illustrating one abnormal position of the elements;

Fig. 4 is another view depicting another abnormal position of the elements;

Fig. 5 is a perspective view of the combustion actuating arm and the bimetal actuator;

Fig. 6 is a front view of a portion of apparatus illustrating the resetting mechanism;

Fig. '7 is a schematic circuit diagram of one form of the invention utilizing a low voltage relay; While,

Fig. 8 isa circuit arrangement illustrating another form of the invention utilizing a line Voltage relay.

s The burner control apparatus includes a metal base 5, suitably formed into the shape illustrated, to provide a supporting means for the various elements comprising the control device. .A metal supporting plate 6 is rigidly secured to the rear side of the base 5 by a series of screws 1. This supporting plate 6 carries-a metal tubular member 8 which is staked at one end to the plate' 6, as shown. A physical condition responsive means, shown here inthe form of an elongated thermal member, is positioned partially within the tubular member 8. It comprises a relatively expansible member 9 which is channel shaped and bent into a U-form with the ends suitably fastened as. by

rivets II to lugs formed on the rear of the supporting plate 6. A relatively 'non-expansible elongated tubular member I2 is arranged `parallel to and between the legs of the U-shaped expansible member 9. One end of the tube I 2 is A rigidly secured by a rivet I3 to the U-bent portion of the expansible element 9, while the other end extends thru an aperture I4 formed in the sup.

porting plate 6 and an additional aperture in the base 5. 'A pair `ofvoppositelyy disposed lugs I5 are slip friction connection which takes the form of a flat spring steel plate I9, is provided between the control arm I8 and the thermal element One end of the plate I9 is secured by.a rivet 2I to the free end of the non-expansible member I2, while the other end is adapted to frictionally slide between a pair of friction blocks 22 disposed on l opposite sides of the plate 'I9. The lower friction block 22 is suitably supported upon an adjusting plate 23, whilenthe upper friction block is suitably supported as shown on a metal plate attached to the control arm I8 together with the spring hinge I6. Guide pins 24 loosely support the adjusting plate 23 to hold it in itsproper position. A stiff compression spring 25 is arranged to bear against the adjusting plate 23 at an angle,

and to hold the friction blocks 22 pressed tightly against the sides of the flat plate I9. An adjusting screw 26 threaded into the control arm I8 is adapted to supply the proper amount of compressive effort to the flat plate I9, and also is arranged at such a'n angle that it prevents any lost motion of the plate 23 around the guide pins 24.

Christiansen, serieu Ne. 236,818, sled october 24, 193s.

i and carries a thermal or warp switch mechanism which consists of a bimetailic actuating strip 36.

' Associated with the bimetal element36 is a pair of bimetal strips 31 arranged parallel to and on opposite sides of bimetal 36 (see Fig. 5) whose function is to compensate bimetal 36 for ambient temperatures. One end of each compensating bimetal element 31 is suitably fastened to the operating arm 21 as shown by means of bolts and nuts 38 and spacing washers. 'I'he other ends of the compensating elements 31 are suitably riveted as shown in Fig. 5 to a stiff metal block 39. One end lof the bimetal element 36 is also riveted to the block 39 in a position between the compensating elements 31. Thus the thermal element 36 is mechanically associated with the arm 21 of the combustion responsive means. A metal block 40 is carried by the bimetal 36. An electric heater 4I is adjustably secured, to the bimetal element 36 by the block 40, between the ends of the bimetal element 36 so that the heater can be shifted to the most advantageous location on the bimetal element. An adjusting screw 42 is provided to hold the heater 4I and the block 49 in the desired position. The metal block 48 has the proper amount of mass to give the bimetal the desired An actuating or operating arm 21, preferably made of a fiat strip of insulating material, is secured to the movable end of the actuating arm I8 by means of a pair of screws 28. In order to limit the motion of the operating arm 21 in either of its directions of movement, a metal stop bracket 29 is provided which is secured by a pair of screws 30 to an insulated mounting plate or panel 3I supported in turn upon the front of the base 5 by means of screws 32. The bottom edge of the operating arm 21 is provided with a slot 33 which straddles the stop bracket 29: A shoulder portion 34 is formed on each side of the bracket 29 which limits the motion of the operating arm in a direction toward the base. This stop constitutes the hot` stop position of the arm 21. In order to limit the movement of the operating arm 21 in'the opposite direction an adjustable screw 35 is threaded into a tumed-up portion of bracket 29 and is engaged by the outer side of the arm 21. This constitutes the cold stop position of the arm/21.

The foregoing combustion responsive elements are arranged and cooperate in such a manner that when the thermal elements 9 and I2 are subjected to the heat from a burner for example,

- their relative movement causes the left-hand end of the tubular member I2 to move so that the control arm I8 is pivoted about its spring hinge encounters either of its stops 34 or 35, depending on its direction of movement, the slip friction means takes effect thru the medium of the steel plate I9 sliding between the friction blocks 22, and the thermal elements can continue to expand or contract without excessive strain. The device therefore operates upon changes in temperature independent of actual temperature. For a more detailed description and operation of the foregoing elements, .and the manner in which the slip friction mechanism is actuatedf reference v may be had to a copending application of William,

- I6, thereby effecting a movement of the operating arm 21 toward the base 5. When the arm 21' ably engage the end of the trigger 44A. The latch member 45 is pivoted by a pin 46 to a U-shaped bracket 41, which is in turn fastened to the rear Y of the insulating plate 3| by screws 48 as shown in Fig. 6. A tensioned coil spring 49. encircles the pivot pin 46 and is arranged to normally urge the latch member 45 man upward or clockwise direction about the pin 46. Adjacent its free end the latch 45 is provided with an aperture 56 large enough for the trigger 44 to slide into under certain conditions. 4A switching meansis provided which preferably takes the form of a contact spring plate 5I- carrying a contact point at its free end and having its other end riveted. as shown, to the pivoted end of the latch 45. A cooperative stationary contact point 52 is riveted to the stop bracket 29. The above arrangement of elements is such disengaged from the end of latch 45 bythe movement of either 'the bimetal 36 or the operating arranged to cooperate with the operating arm 21 to either maintain the trigger 44 in engagement with' the latch 45 or tok release the same and thereby open the contacts 5I and 52. Normally the elements are'postioned as shown in Fig. 1.v and in the normal operation of the control de- The operating arm 21 has associated with it' that when the trigger 44 is vice the electric heater 4|is usually first energized, thereby e'ecting a warping action of the bimetal element 36, tending to move its trigger end 44 outward toward the left in sliding engagement across the top of the latch 45. During a predetermined time interval combustion conditions are usually established in the burner, and the thermal elements 9 and I2 are actuated to swing the operating arm 21 inward in a direction toward the base 5 until the stopA 34 is encountered. Since the bimetal element 36 is secured to and carried along by the movement ofthe operating arm 21, it is apparent that the trigger 44 tends to move inward with the operating arm 21 across the top of latch 45 in opposite direction to the warping movement of the bimetal 36,- and the relative initial position of the trigger upon the end of the latch is substantially maintained so that the latch is held restrained. The ultimate position assumed by the elements is shown in Fig. 2. The adjusting screw 43 is provided in order to properly calibrate the exact position of `the trigger 44 upon the latch end 45 relative to the operating arm 21 when the bimetal 36 is in its hot position. Under the foregoing assumed conditions the contacts 5I and 52 are maintained in their closed condition.

Assume now that the control elements are in their normal inactive positions and that the warping action of the bimetal element 36 has begun under the action of the electric heater 4|.

vAssume further that after a definite time interval l the operating arm 21fails to move inward and remains against its cold stop 35 due to the absence of relative motion between the thermal elements 9 and I2. Under these conditions the bimetal element 36 warps off the left hand end of latch 45 and permits the latch to snap upward under the tension exerted upon it -by the coil spring 49. The upward movement of latch 45 results in opening the switch or control contacts 5I and 52. The resultant position of the ele- 40- associated with the heater 4| The opening of contacts 5| and 52 effects a disabling function of the burner as will be pointed out hereinafter.

In order to reset the latch 45 after it has been tripped into its open circuit position, a resetting lever 53 (see Fig. 6), preferably made of insulating material, is provided. It is pivoted between the base 5 by screws 32, as shown. The resettinglever 53 is preferably provided at its operating end with suitable projecting portions, as shown. The uppenprojecting 'portion is normally in engagement with the lower reset contact 55 in their closed position: A coil spring 56, havments under these conditions is shown in Fig. 3. .I

Under another condition of operation, assume that for some reason the electric heater circuit' opens, or the heater 4I becomes disabled in some manner. The bimetal element 36, as a result,

' fails to eiect a warping action, and upon the establishment of combustion in the burner the operating arm 21 moves inward. The trigger 44 slides and is moved along with the operating arm 21 until it falls thru the aperture 50 in the latch whereupon the latch 45 snaps upward to open contacts 5| and 52. The ultimate position of the elements under .these conditions is shown in Fig. 4.

The adjusting screw 35 vmay be turned in or out to properly calibrate the normal position of the operating arm 21 so that the trigger 44 may be located in the desired position on the catch 45 somewhere between its free end and the edge of the aperture 5|). It may be desirable that the trigger 44 be normally positioned closer to either the aperture or the end of the latch 45 for reasons which will be now pointed out.

From the foregoing description it will be apparent that the distance over which the trigger- 44 travels. across the end of latch 45, and before it releases the latch, corresponds to the lapse of a definite time interval during which certain necessary functions in the operation of the burner must take place. The length of time required for the latch 45 to trip is, therefore, set by adjusting the travel of trigger 44 on the latch 45.

The rate of travel of the bimetal is governed by the size ofthe bimetal 36 and that of the block may be accomplished in one manner by providing ing one end secured to the reset lever arm 53 and the 'other end Ito the insulating plate 3 I, normally holds the reset lever against the reset contacts 55. In resetting thelatch 45 the free end of the reset lever 53 is 'manually moved upward. This action first causes the reset contact springs 55 to open, due tov the residual tension stored in the lowermost one of the reset springs 55, and secondly causes the reset lever to engage the top side of the latch 45 forcing it downward asufficient distance beyondthe end of the trigger 44 so that the trigger is enabled to pass over the end of latch 45 and can then assume a position on top of the latch 45. Y At the'same time the contacts 5I and 52 are closed. Releasing the reset lever 53 permits vthe, free end to snap downward under tension of coil spring 56 while the other end closes reset contact springs 55. From the foregoing it will he apparent that during the time of the full. movement of the reset lever to reset the latch 45 the reset contact springs 55 are maintained opened. The purpose of this will be hereinafter pointed out more fully.

It is necessary that the action of the bimetal element 36 be so correlated or calibrated with respect to the action of the operating arm 21 under control of the thermal elements 9 and I2 that the trigger. end 44 be maintained properly in engagement with the free end of the latch 45 under all assumed conditions of operation and for any type of installation. Since the operating characteristics of the bimetal eleient 36 un'- a slidable sleeve or tube member 6I on the out- -the complete control unit upon a furnace or burner chamber. l

In order to prevent the entrance of combustion gases into the *region of the slip friction mechanism and to prevent the passage of coldair over the thermal elements\9 and I2, a washer member 64 of suitable shape passes over the thermal elements 3 and I2 to enclose the end of tube 6. For the same reason the aperture I4 is made only sufliciently large to allow free movement of the tubular element I2.

In Figs. '1 and- 8 there is disclosed circuit arrangements incorporating the previously described mechanism. Referring particularly to Fig. 7, the arrangement diagrammatically illustrates a burner installation including various operating devices to which a source of line voltage current is fed over the line wires 66 and 61. Connected across the line wires thru safety switch contacts5I, 52 and reset contacts 55 is a primary winding 68 of a step down transformer.

"I'he low voltage secondary winding 69 is `connected in series with a room thermostat 1I thru its contacts 12. The low voltage circuit likewise includes a relay 13 which upon energization closes motor contacts 14. A fuel burner motor 15 is connected in series with the motor contacts 14 and the line conductors 66 and 61. Suitable ignition means 16 is connected in parallel with the motor'15. The resetting contacts 55 of the con- 5 tion of the elements after this action is shown in Fig. 2.

Should combustion conditions not be satisfactorily established within a predetermined time,y

say 90 seconds, there can be no motion'of .the

actuating arm 21, and the trigger 44 releases trol device of Fig. 1, and thesafety lockout contacts 5I and 52, are connected in series relationship with the line conductor 66. The electric heater 4I for bimetal element 36 is connected in the low voltage circuit across the secondary winding 69 by the thermostat 1I. For the sake of clearness this electric heater 4I has been shown detached from its normal position upon the bimetal 36. The remaining elements comprising the control device of Fig. 1 have also been illustrated in a simplified diagrammatic manner. To safeguard and shut down the system in the event that excessive temperatures are produced in the furnace, a limit control switch 16a may be inserted in the line 66.

In the normal operation of the burner control system assume all of the control elements are in their normal inactive positions as indicated in Fig. 1. Assume now that in response to a call for heat in the room where the thermostat 1I is located, a closure of its contacts 12 is-effected. Low voltage current is accordingly fed from the secondaryv winding 63 of the transformer thru the winding of relay 13, and the electric heater 4I in parallel therewith. The energization of relay winding 13 effects a closure of-motor contacts 14, thereby closing the circuit to the fuel burner 15, and the ignition means 16, to activate the fuel burning means and establish combustion in the burner. The electric heater 4I is likewise energized in the foregoing circuit, and is effective to heat the bimetal element 36 to produce a warping action, tending to move the trigger 44 in a left-- handdirection across the end of the latch 45. In response to combustion the thermal elements 3 and I2 of the control device are normally lactuated. The actuation of the thermal elements 3 and I2 moves the actuating arm 21 in 'a direction tending to oppose the movement of the free end of the bimetal element 36. Now if the control is in proper adjustment, the Ifixed end of bimetal 36. which is indirectly fastened to the actuating arm 21, moves in one direction approximately as fast as the free end of bimetal 36 moves in the opposite direction, and as a result the trigger 44 remains practically stationary on the latch 45. For satisfactory operation, the rate of heating or cooling of the 'stack elements 6 and I2 relative to that of the bimetal element 36 is adjusted by means of the sleeve 6I so that the trigger 44 does not trip the latch 45 by moving past the end of the-latch 45 or over the aperture 5I. After the latch 45. The control elements then assume the position shownin Fig.3. Responsive to the release of the latch the safety switch contacts 5I and 52 are opened, thereby interrupting the line circuit 66 and disconnecting the energizing source from the transformer primary 65, the fuel motor 15, and ignition means 16. The heater 4I and the relay 13 likewise are no longer energized, and as a result the bimetal element 36 cools oi. The

0 latch 45 being'tripped to its open position, the burner apparatus is ineffective to be again actuated until the safety switch is manually reset. In order to render the system again operative,

the reset lever 53 must first be manually operated 5 which resets the latch 45 under the trigger 44 and closes the safety contacts 5I and 52 to complete the line circuit. During this resetting operation, however, the resetting contacts 55 are opened, thereby precluding the possibility of' manually holding orl plugging up the reset lever 53 in such a'. manner as to make the system operate independent of the safety switch and thus create hazardous conditions.

Under the foregoing conditions, if combustion is successfully established, the burner functions to operate continuously as long as the thermostat contacts 12 are closed. A rise in room temperature effects the thermostat 1I and causes it to open its contacts 12, thereby interrupting the o circuit thru the heater 4I and relay winding 13. The. opening of relay contacts 14 disconnects the burner, and accordingly combustion ceases and the stack elements 9 and I2 cool olf.

After the burner has been functioning northe hot stop 34, assume that for some reason the heater becomes disabled while the burner is running or Athat the actuating arm remains in its hot position after the thermostat opens its contacts. In either event the bimetal elerment 36 cools and shuts down the system as shown in Fig. 4 by releasing the latch 45 which in turn opens the safety switch contacts 5I and Assume now, for example, that the burner has been operating satisfactorily for some time, and that due to lack of oil supply, or some other reason, the stack elements 3 and I2 cool off while the heater 4I remains energized. In this case the operating arm 21 moves outward toward its 6 colw' stop 35, carrying-the bimetal element ze along with it. The trigger 44 slips over the end of `latch 45 in the position shown in Fig. 3, and

the burner is accordingly shut down when con- 5 tacts 5I and 52 open.

An alternate circuit position for the electric heater 4I is shown in dotted lines in Fig. 'l in which it is connected directly between the motor relay contacts 14 and the line wire 61. This may be used in the event that a line voltage heater l is desirable. -Under certain conditions it may be desirable to install the system without utilizing the low voltage circuit for the thermostat 1I. In this case the relay 1: and the transformer 6x4-ts are eliminated and the thermostat 1I has its conmally and the operating arm 21 is resting against y entire load on the control as in'Flg. '1.

tacts 12 connected directly in series with the line conductorsv 66 and 61 in the same position the relay contacts 14 are now connected.

From the foregoing it is apparent that the control system disclosed in Fig. 7 checks the operation of the stack switch in both Athe hot and cold directions, and shuts down the entire system if the stack switch does not go thru its complete cycle of operation for every cycle of operation of the fuel burning means. Additionally, in the event the heater 4I for the bimetal element 36 becomes disabled in any way, the .entire system is shut down. The ability of the device tov shut down the system -in the event of .failure of any of its essential elements is an important feature of the invention.

Another important feature of the invention is the4 method of independently energizing the heater in such a way so as to be in no way dependent upon the energization of the fuel burning means and yet shut the system down in the event the heater becomes disabled. When a relay is not used, by utilizing this feature a control may be built Without connecting the safety switch heater in series with the electrical burner load.

.This departure fromthe conventional series heater arrangement enables one design ofsafety switch heater to be used regardless of the size of motor used.

Referring now particularly to the modified circuit arrangement disclosed in Fig. 8, in this arrangement, it is not necessary to eiect a lockout operation in either of two directions in order to check the operation of the heater 4I. In Fig. '7 it will be recalled the electric heater 4I was connected in the low voltage circuit in parallel with the relay winding 13, and hence was energized totally independent of the relay or fuel burning means, and in the event the heater became disabled, the "trigger 44 was moved into the aperture 50 of the latch 45 by the actuating arm 21 to effect a lockout. In Fig. 8, however, theheater 4| is connected in series circuit with the thermostat contacts 12 and the low voltage secondary winding'11 of a choke coil having its primary Winding 18 connected with relay winding 13 across the line conductors 66--61. In this manlner operation of the relay is dependent upon circuit continuity thru the heater. Now in the event the heater 4| becomes disabled it eii'ects a cooling action of the bimetal element 36, but in this instance it is not necessary to effect a lockout condition of the latch 45 wherein the trigger 44 snaps into the aperture 50, because the opening of the circuit passing thruthe heater 4I and including the thermostat 1I and the secondary of the choke 11, eects a choking reaction of the current in the primary winding 18 so that the relay winding 13 is substantially deenergized and it releases its motor contacts ,14, thereby effecting a shut-down of the system.` In this modiiication the operating arm 21 effects alockout movement oflatch 45 in the same manner as in Fig. 7 in the event that there is a failure of ignition ori-combustion in the burner either upon starting or during the running of the same. The

" two position lockout latch can be used with this ready pointed out in connection withthe description of the operation of Fig-7. The resetting contacts 55 and the safety switch contacts and 52 are shown in series with the relay winding 13 rather than in series with the While only Ia preferred form of the invention has been illustrated and described, it is conceivable that certain modications of the same may be made by those skilled in the art but consistent with the broad principles of the invention; and, it is. therefore, desired not to limit the invention to the exact disclosure but only vto the scope of appended claims.

What is claimed is:

1.- In a burner control system of the class described, a burner motor, means for initiating the operation of the motor, a thermal element, a heater'for said thermal element for actuating the same, a latch member released by the opera'- tion of the thermal element, combustion responsive means mechanically connected with said thermal element for operating the same in response to combustion conditions for maintaining the latch in restraint, said latch also released by the independent operationof the combustion responsive means when the thermal element is not actuated, and a switch controlled by the movement of thelatch for disconnecting the burner motor.

2. A bu'rner control system of the class described, a burner motor, means for initiating the operation of the burner motor to produce combustion conditions, a thermal element, a

heater energized by the motor initiating means for heating the thermal element, a safety switch controlled by the thermal element and effective to disconnect the motor when operated, and combustion responsive means forming a mechanical actuating connection with said thermal element for imparting a compensating movement to said thermal element and thereby preventing the thermal element from actuating the safety switch while permitting continued movement of the thermal element through a limited range.

3. In a burner control system of the class described including a fuel motor and a safety switch for disconnecting the fuel motor, an electric heater, means for energizing the heater and the fuel motor together, a thermal element actuated by the heater to open the safety switch and disconnect the fuel motor, combustion responsive means, mechanical means connecting the combustion responsive means with the thermal element to render the thermal element ineffective to op'en the safety switch in casecombustion is established by the fuel motor, said combustion responsive'means arranged to `open the safety switch in case the thermal elem nt is not actuated by the heater, and means for restoring the safety .switch to its normal position for re-operating the burner.

4. In a burner control systeml of the class described, a burner motor, means for starting the operation of the burner motor bustion conditions, a thermal element, a heater operated. by the burner. starting means for actuating said thermal element, a combustion responsive element mechanically associated with the thermal element, and a safety switch for stopping the operation of the burner motor and maintained closed by the joint operation of the combustion, responsive means and the thermal element, and opened by the independent operation of either the combustion` responsive means or the thermal element.-

5. In a burner control system of the class described, a` burner motor, a room thermostat for lstarting the operation of the burner motor; an lactuating arm, means responsive to tlie establishment of combustion by to produce com the burner motor for operating the actuating arm, a thermal element connected to the actuating arm, an electric heater for heating the thermal element and energized by operation of the room thermostat independently of the motor, a safety switch controlling the operation of the burner motor, means cooperating with the safety switch and thermal element whereby' the safety switch is maintained normally closed responsive to the joint operation of the actuating arm and the thermal element, and is released to disconnect the burner motor responsive to the independent operation of the actuating arm or the thermal element.

6. In a burner control system of the class de'- scribed, fuel burning means, means for stopping and starting the burner motor, an actuating arm, condition responsive means for operating said actuating arm in response to the establish- .ment of combustion by the fuel burning means, a thermal member supported on the actuating arm, electric heating means energized with the fuel burning means for operating said thermal member, a safety switch for disconnecting the fuel burning means, and means responsive to the independent operation of either the actuating arm or the thermal member for opening the safety switch, said means also responsive to the joint operation ofthe actuating arm and the thermal memberv for maintaining the safety switch closed.

'1. In a burner control system of the class described, a burner motor, a safety switch for disconnecting the burner motor when opened, a latch for controlling the safety switch,.a thermal element normally holding said latch inrestrained position, an electric heater energized during the operation of the burner motor for heating the thermal element to cause movement thereof to release the latch,.combustion respons ve means for operating the thermal element in another direction of movement to also release the latch, and means for holding the latch restrained in case both the heater and the combustion responsive means are actuated at the same time.

8,. In aburner control system of the class described, fuel burning means, means for initiating the operation of the fuel burning means, an actuating arm, condition responsive meansI rendered effective with the establishment of combustion by the fuel burning means for operating said actuating arm, a thermal member arranged on the actuating arm, electric heating means ener- \gized with the fuel burning means for operating said thermal member, a closed safety switch associ ted with said actuating arm and said thermal m ber for disconnecting the fuel burning means whn opened, and cooperating means controlled \vy he actuating arm and the: thermal member hereby said safety switch is opened responsive to the independent operation of either the actuating arm or the thermal member and is maintained closed responsive to the joint operation of the actuating arm and the thermal member.

9. In a burner control system of the class described, a fuel burning means, an electric heater, a thermostatic switch, separate independent circuit connections extending from the thermostatic switch to the fuel burning means and the electric heater for independently energiring the same, a normally closed safety switch, a circuit connection including the safety switch and the thermostatic switch for deenergizing the fuel burning means and the electric`- heater when either of the switches are open,- a thermal element operated in one direction by the energization of the electric heater to open the safety switch, combustion responsive means mechanically connected to the thermal element for operating the thermal element in another direction to prevent the opening of the safety switch, said combustion responsive means effective to operate the thermal element to open the safety switch in controlled by the switch.

ll. In a burner control apparatus of the class described, an actuating arm, combustion responsive means for operating said actuating arm, a thermal element, means for supporting said thermal element upon said actuating arm, an electric heater for actuating said thermal element, a pivoted latch having slidable engagement with the end of saidthermal element, said latch being held restrained responsive to the joint operation of the thermal element and the actuating arm, but released responsive to the independent operation of the actuating arm or the thermal element, and switching mechanism controlled by the release of the latch.

12. In a burner control apparatus, an actuating arm, combustion responsive means for operating .said actuating arm, a thermal member carried on the actuating arm, electric heating means for operating said thermal member, a safety switch,

Asaid safety switch including means cooperative with the operation of the actuating arm and the thermal member whereby the safety switch is opened responsive to the operation of either the actuating arm or the thermal member alone after the lapse of a time interval, and is maintained closed responsive to the Joint operation of both the actuating arm and the thermal member.l

13. In a' burner control apparatus of the class described, an actuating arm, a thermal element carried on one end of the actuating arm, a pivoted latch having slidable engagement with one end of the thermal element, means for operating the actuating arm in one direction to move the thermal element in sliding engagement with the latch to release the same, means for operating the thermal element in the` opposite direction to prevent the release of the latch, a switching means operated by the release of the latch, and means for resetting said latch and operating said switching means to its normal. position.

14. In a burner control apparatus of the class described, an actuating arm, a thermal element connected to said actuating arm and movable a pivoted latch member having slidable engagement with the end of the thermal element whereby the joint operation of the actuating arm and the thermal element is effective to maintain the latch member restrained and the independentsv j operation ofthe actuating member or the thermal element is effective to release the latch member, switching means controlled by the release of the sponsive means, a thermal element supported upon the free end of said actuating arm and movable thereby, an electric heater for said thermal element effective to move the thermal elementin a direction opposite to the movement of the actuating arm, a burner motor, means for initiating the operation of said burner motor, said electric heater energized in response to the motor initiating means, a latch associated with said thermal member whereby the joint operation o f the actuating arm and said thermal member maintains the latch restrained. and whereby upon the failure of combustion or disabling of the heater the latch is released, and a safety switch operated by the release of the latch to disconnect the burner motor.

16. In a burner control apparatus of the class described, a combustion responsive means, an

-actuating arm connected thereto, slip friction means connecting the actuating arm with the combustion responsive means, a thermal element,

means for supporting said thermal element from the end of the actuating arm, a latch, a heater for operating said thermal element, said latch i arm and movable therewith, an electric heater for operating said thermal element, a latch member having a portion thereof in sliding relationship with the end of said thermal member, the

joint operation of said actuating arm and saidv thermal element being eective to maintain the thermal element upon the end of the latch member to hold it restrained, the operation of the thermal member or the actuating arm alone being effective to release the end of the thermal element from the latch member, means for operating the latch member upon its release, manp ual means for restoring said latch member in engagement with the thermal element, and a switching mechanism controlled by -the movement of the latch member.

18. In a burner control apparatus of the class I described, a combustion responsivev means, an actuating arm operated thereby, a thermal element secured to the actuating arm and arranged to be moved thereby, means for heating the ther... mal element to cause actuation thereof independent of the movement of the actuating arm', a safety switch latch member for stopping the burner apparatususaid latch member arranged to released bythe independent operation of element, and adjusting means for correlating the time of response of the actuating arm and the thermal element.

19. In a burner control apparatus of the class described, combustion responsive means, an actuating arm, a slip friction connecting means between the combustion responsive means and the actuating `arm for operating the actuating arm, adjustable'stop means for limiting the operating movement of the actuating arm, said slip friction means taking effect after the actuating arm engages the stop means, a thermal element supported uponand carried along with the actuating arm in its operating movements, means for operating the thermal element independently of its movementby the actuating arm, a closed safety switch for stopping the operation of the burner apparatus when opened, switch arranged to be maintained closed responsive to the joint operation of the actuating arm and the thermal element and opened responsive to the independent operation of either the actuating arm or the thermal element, and adjustable stop I.means on the actuating arm for adjusting the thermal element with respect to the actuating arm.

20. In a burner control system of the class de- `scribed, a burner motor, condition responsive means controlling the energization of the burner motor, an 'actuating arm, combustion responsive means for mechanically operating the actuating arm,` a thermal element, an electric heater for heating the thermal element and controlled in a predetermined relationship with the burner I apparatus is operated, said actuating arm andv thermal element arranged to be operated jointly.

during the normal operation of the burner apparatus but independently of each other in response to abnormal operations of the burner apparatus, a closed safety switch latch cooperating with the `actuating arm and the thermal element for disconnecting the burner apparatus when opened, said safety lswitch latch having a portion thereof in slidable restrained engagement with the thermal element whereby upon the independent operation of thethermal element the thermal element slides oif one end of the latch portion to release the latch and upon the independent operation of the actuating arm the thermal element slidesoi of the other end of the latch portion to release the latch, and whereby upon the joint operation of the actuating armand the thermal element the thermal element is maintained relatively'stationary upon the latch portion to maintain the latch restrained.

either the actuating arm or the thermal ele- A ment and maintained closed by the joint operation of the actuating arm and the .thermal 22. In a combustion control system, a fuel feeding motor, an electric circuit for the motor,

-a lockout switchcontrolllng tlie circuit to the motor, a thermal element for actuating the lockout switch, a heater for the thermal element connected in parallel with the motor, condition responsive means controlling the circuit to-the motorv and heater,y and combustion responsive` said safety A means for mechanically actuating the lockout switch, said lockout switch thermal element and ,combustion responsive means cooperating to I"'nnatintain the lockout switch closed responsive for the thermal element connected in parallel with the relay, condition responsive means controlling the circuit to the relay and heater, and combustion responsive means for mechanically actuating the lockout switch, said lockout switch thermal element and combustion responsive means cooperating to maintain the lockout switch closed responsive to the actuation of both the thermal element and the combustion responsive means and cooperating to open the lockout switch responsive to the independent actuation of either the thermal element or combustion.

responsive means.

VIRGIL ROBINS, TATE. 

